Ytterbium complexes compounds

Further reactions of iodo complexes 158 and 160 with KN(PPh2) in THF led to heteroleptic compounds [Ln(L30) N(PPh2) (THF)] (Ln = Eu (161), Yb (162)) [95]. An alternative reaction pathway (Scheme 59) started from the triva-lent ytterbium complex 156 which already contained both ligands L30 and the... 

In the quite different chemistry of the lanthanides we have used a conceptually similar approach to prepare cage complexes of the lanthanides from which the metal ion cannot escape without breaking a C—C or C—N bond. The proposed structure for such a ytterbium complex is shown in Figure 3. This complex is relatively hydrolytically stable. In contrast, the intermediate compounds with 1 or 2 methylene bridges are readily hydrolyzed since they allow ready exit of the metal ion. The structures of several of these intermediates have been determined. 

In order to study a bis[8]annulene compound with a divalent central metal atom we have synthesized and characterized the divalent ytterbium complex K2[Yb(CgHg)2]F K2[Yb(CgHg)2]r and its calcium analogue, K2[Ca(CgHg)2].51 These compounds were prepared by a reaction which utilizes the solubility of ytterbium and calcium metals in liquid ammonia. Reaction of cyclooctatetraene, potassium and either ytterbium or calcium, in liquid ammonia solution, gives the desired potassium salt of the complex dianion. 

The binuclear samarium and ytterbium complexes with mixed valence of Ln(II, IQ) (Me5C5)2Sm( i-Cp)Sm(C5Me5)2 [37] and (Me5C5)2Yb(ji-F)Yb(C5Me5)2 [46], are close to the being considered class of compounds in their nature. The complex with cyclopentadienyl bridge can be isolated from the mixture containing cyclopentadiene and... 

The binuclear ytterbium complex Cp3YbNC4H4NYbCp3 is obtained by the treatment of benzene solution of ytterbium tricyclopentadienide with pyrazine [71]. The complex has a surprisingly high volatility for such a type of compounds its sublimation starts at 75°C in vacuum. The coordination N — Yb bond is relatively weak. It is cleft by THF, which easily replaces pyrazine. By the same reason the ions with a metal-pyrazine moiety are... 

For the preparation of ytterbium complexes Cp2YbX the oxidation of dicyclopenta-dienylytterbium by compounds of Tl, Cu, Hg and Ag is offered [67] ... 

Not only persistent radicals can be reacted with low-valent metal complexes but also those that are generated in situ by the thermal cleavage of peroxides. To our best knowledge, so far, only samarium [41] and ytterbium [42] compounds were reported into which a tm-butoxide moiety was introduced by reduction of di-rcrr-butylperoxide by the metal center. Here, the first Cp-type titanium monoalkoxide complex synthesized by reacting a titanium(lll) species with di-tert-butylperoxide is reported. 

Recently, hydride complexes supported by guadinate ligands 56 and 57 were found to be active in styrene polymerization, but only for the smaller lanthanides [30,31]. Both the lutetium and the ytterbium complexes show low conversion rates (the Lu compound converts 100 equiv within 3 days) the products are highly syndiotactic, and the polymer produced by the ytterbium compound was reported to have a high melting temperature of 289-293 C (Af = 90,000 g/mol, MJM = 2.6). 

A) approximate a tetrahedral arrangement. The bulkiness of the ligands in this case must also impose a severe steric requirement on the complex. Although the analogous ytterbium complex could be prepared and is isomor-phous with the lutetium compound, complexes with the lighter lanthanides could not be synthesized. 

While ytterbium(II) benzamidinate complexes have been known for many years/ the synthesis of the first divalent samarium bis(amidinate) required the use of a sterically hindered amidinate ligand, [HC(NDipp)2l (Dipp = C6H3Pr2-2,6)/ As illustrated in Scheme 54, the dark green compound Sm(DippForm)2(THF)2 (DippForm = [HC(NDipp)2] ) can be prepared by three different synthetic routes. Structural data indicated that hexacoordinated... 

For further contributions on the dia-stereoselectivity in electropinacolizations, see Ref. [286-295]. Reduction in DMF at a Fig cathode can lead to improved yield and selectivity upon addition of catalytic amounts of tetraalkylammonium salts to the electrolyte. On the basis of preparative scale electrolyses and cyclic voltammetry for that behavior, a mechanism is proposed that involves an initial reduction of the tetraalkylammonium cation with the participation of the electrode material to form a catalyst that favors le reduction routes [296, 297]. Stoichiometric amounts of ytterbium(II), generated by reduction of Yb(III), support the stereospecific coupling of 1,3-dibenzoylpropane to cis-cyclopentane-l,2-diol. However, Yb(III) remains bounded to the pinacol and cannot be released to act as a catalyst. This leads to a loss of stereoselectivity in the course of the reaction [298]. Also, with the addition of a Ce( IV)-complex the stereochemical course of the reduction can be altered [299]. In a weakly acidic solution, the meso/rac ratio in the EHD (electrohy-drodimerization) of acetophenone could be influenced by ultrasonication [300]. Besides phenyl ketone compounds, examples with other aromatic groups have also been published [294, 295, 301, 302]. 

The compounds Ln(C5H5)2Cl also have been made only with the lanthanides above samarium (772). These compounds are stable in the absence of air and moisture, sublime near 200 °C, are insoluble in non-polar solvents, and exhibit room temperature magnetic moments near the free ion values (772, 113). The chloride ion may be replaced by a variety of anions including methoxide, phenoxide, amide and carboxylate. Some of these derivatives are considerably more air-stable than the chloride — the phenoxide is reported to be stable for days in dry air. Despite their apparent stability, little is known about the physical properties of these materials. The methyl-substituted cyclopentadiene complexes are much more soluble in non-polar solvents than the unsubstituted species. Ebulliometric measurements on the bis(methylcyclopentadienyl)lanthanide(III) chlorides indicated the complexes are dimeric in non-coordinating solvents (772). A structmre analysis of the ytterbium member of this series has been completed (714). The crystal and molecular parameters of this and related complexes are compared in Table 5. 

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